U.S. patent number 11,108,470 [Application Number 16/369,625] was granted by the patent office on 2021-08-31 for optical channelizer for w-band detection.
This patent grant is currently assigned to Northrop Grumman Systems Corporation. The grantee listed for this patent is Northrop Grumman Systems Corporation. Invention is credited to Anastasios P. Goutzoulis, Doyle T. Nichols.
United States Patent |
11,108,470 |
Goutzoulis , et al. |
August 31, 2021 |
Optical channelizer for W-band detection
Abstract
An optically-downconverting channelizer is disclosed for W-band
detection. The channelizer includes an input waveguide configured
to carry an inputted signal having a plurality of wavelengths
including a desired wavelength and a plurality of ring resonators
arranged in parallel and coupled at spaced apart locations along
the input waveguide for receiving the inputted signal, wherein each
of the plurality of ring resonators is configured to pass a
selected wavelength signal to an output end. The channelizer
further includes a control waveguide that carries a second signal
having a wavelength that differs from the desired wavelength by a
predetermined amount, and a plurality of detectors coupled to
respective output ends of the ring resonators, the plurality of
detectors configured to produce channelized RF output signals
representative of desired RF bands.
Inventors: |
Goutzoulis; Anastasios P.
(Annapolis, MD), Nichols; Doyle T. (Ellicott City, MD) |
Applicant: |
Name |
City |
State |
Country |
Type |
Northrop Grumman Systems Corporation |
Falls Church |
VA |
US |
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Assignee: |
Northrop Grumman Systems
Corporation (Falls Church, VA)
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Family
ID: |
1000005772643 |
Appl.
No.: |
16/369,625 |
Filed: |
March 29, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190229815 A1 |
Jul 25, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13923697 |
Jun 21, 2013 |
10447409 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
10/90 (20130101); H04B 2210/006 (20130101) |
Current International
Class: |
H04B
10/90 (20130101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003163634 |
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Jun 2003 |
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JP |
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WO-2005/064375 |
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Jul 2005 |
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WO |
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Other References
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Primary Examiner: Radkowski; Peter
Attorney, Agent or Firm: Alston & Bird LLP
Claims
What is claimed is:
1. A method for signal channelizing comprising: receiving, by an
input waveguide, an inputted signal having a plurality of
wavelengths including a desired wavelength, wherein the inputted
signal comprises a single carrier signal; filtering the inputted
signal through each of a plurality of ring resonators to pass a
selected wavelength signal to a respective output end, wherein the
plurality of ring resonators are arranged in parallel and coupled
at spaced apart locations along the input waveguide for receiving
the signal; receiving, by two control waveguides, two signals
having wavelengths that differ from the desired wavelength by a
first predetermined amount and a second predetermined amount
respectively; and producing, by a plurality of detectors,
channelized RF output signals representative of desired RF bands,
wherein each of the plurality of detectors is coupled to a
respective output end of one of the ring resonators and to one of
the two control waveguides.
2. The method of claim 1, wherein the inputted signal comprises
inputted RF signals modulated onto the single carrier signal.
3. The method of claim 1, wherein the desired wavelength is a
wavelength of the single carrier signal.
4. The method of claim 1, wherein the first predetermined amount is
different from the second predetermined amount.
5. The method of claim 1, wherein the two control waveguides are
coupled to distinct subsets of the plurality of detectors.
6. The method of claim 1, wherein the frequency range of the
channelized RF output signals is smaller than the frequency range
of the inputted RF signals.
7. The method of claim 1, wherein each of the plurality of
detectors is configured to produce a channelized RF output signal
by heterodyning the signal from the control waveguide to which it
is coupled with the selected wavelength signal from a respective
output end of one of the ring resonators.
8. The method of claim 1, further comprising: receiving, by one or
more additional control waveguides, one or more signals having
wavelengths that differ from the desired wavelength by
predetermined amounts, wherein at least one of the plurality of
detectors is coupled to each of the one or more additional control
waveguides and is configured to produce a channelized RF output
signal by heterodyning the signal from the control waveguide to
which it is coupled with the selected wavelength signal from a
respective output end of one of the ring resonators.
9. The method of claim 1, wherein the desired wavelength comprises
a W-band wavelength.
10. The method of claim 9, wherein the first and second
predetermined amounts comprise at least 75 GHz.
11. The method of claim 1, wherein at least one of the ring
resonators includes a plurality of rings.
12. The method of claim 1, wherein the ring resonators comprise
micro ring resonators.
13. The method of claim 1, further comprising creating the inputted
signal for the input waveguide by modulating, by an optical
modulator, an inputted optical carrier signal with a received
signal.
14. The method of claim 1, wherein receiving the inputted signal by
the input waveguide, filtering the inputted signal, receiving the
two signals by the two control waveguides, and producing the
channelized RF output signals occur on a single chip.
15. The method of claim 1, wherein the two signals received by the
two control waveguides are from at least a source distinct from the
input waveguide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This patent application claims priority to U.S. patent application
Ser. No. 13/923,697, filed Jun. 21, 2013, the contents of which are
incorporated herein by reference in their entirety.
TECHNOLOGICAL FIELD
Example embodiments of the present invention relate generally to
radio wave detection and, more particularly, to an optical
channelizer for optically downconverting input signals for W-band
detection.
BACKGROUND
Recent advances in the area of integrated optical technology have
resulted in improvements to integrated optical channelizer (IOC)
technology. At the same time, the millimeter wave (mmW) spectrum,
and in particular, the W-band (75-110 GHz) has become increasingly
relevant as the latest "new" threat band.
BRIEF SUMMARY
Because of the growing potential for threats detectable in W-band
spectrum, embodiments of the present invention address what is
likely to develop into an important need to detect signals in the
W-band spectrum. Accordingly, example embodiments of the present
invention describe an optically-downconverting optical channelizer
for W-band detection with up to a 100% probability of intercept.
The focus on W-band notwithstanding, the optically-downconverting
optical channelizer has an inherent bandwidth (BW) that exceeds
4,000 GHz. Although any of its filters can be tuned anywhere in
this 4,000 GHz band, example embodiments described below are used
for threat detection in the millimeter wave (mmW) spectrum, and
specifically in the W-band (75-110 GHz).
In a first example embodiment, a signal channelizer is provided
that includes an input waveguide configured to carry an inputted
signal having a plurality of wavelengths including a desired
wavelength, and a plurality of ring resonators arranged in parallel
and coupled at spaced apart locations along the input waveguide for
receiving the inputted signal, wherein each of the plurality of
ring resonators is configured to pass a different selected
wavelength signal to a respective output end. The signal
channelizer further includes a control waveguide that carries a
second signal having a wavelength that differs from the desired
wavelength by a predetermined amount, and a plurality of detectors
coupled to the respective output ends of the ring resonators, the
plurality of detectors configured to produce channelized radio
frequency (RF) output signals representative of desired RF
bands.
In some embodiments, each of the plurality of detectors is coupled
to the control waveguide and is configured to produce a channelized
RF output signal by heterodyning the second signal with the
selected wavelength signal from a respective output end of one of
the ring resonators.
In other embodiments, the signal channelizer includes one or more
additional control waveguides that carry signals having wavelengths
that differ from the desired wavelength by predetermined amounts.
In such embodiments, each of the plurality of detectors is coupled
to one of the control waveguides and is configured to produce a
channelized RF output signal by heterodyning the signal from the
control waveguide to which it is coupled with the selected
wavelength signal from a respective output end of one of the ring
resonators.
In some embodiments, the desired wavelength must be such that
allows operation at W-band. In such embodiments, the predetermined
amount may be 75 GHz. In other embodiments, at least one of the
ring resonators includes a plurality of rings. In another
embodiment, the ring resonators comprise micro ring resonators. In
yet another embodiment, the signal channelizer includes an optical
modulator configured to create the inputted signal for the input
waveguide by modulating an inputted optical carrier signal with a
received signal. In a further embodiment, the signal channelizer is
contained on a single chip.
In another example embodiment, a method for signal channelizing is
provided. The method includes receiving, by an input waveguide, a
signal having a plurality of wavelengths including a desired
wavelength, and filtering the signal through a plurality of ring
resonators, arranged in parallel and coupled at spaced apart
locations along the input waveguide for receiving the signal, to
pass selected wavelength signals to a respective output end. The
method further includes receiving, by a control waveguide, a second
signal having a wavelength that differs from the desired wavelength
by a predetermined amount, and producing, by a plurality of
detectors coupled to the respective output ends of the ring
resonators, channelized RF output signals representative of desired
RF bands.
In some embodiments, each of the plurality of detectors is coupled
to the control waveguide. In such embodiments, producing
channelized RF output signals representative of desired RF bands
includes heterodyning, by each of the plurality of detectors, the
second signal with a selected wavelength signal from a respective
output end of one of the ring resonators.
In other embodiments, the method includes receiving, by one or more
additional control waveguides, one or more signals having
wavelengths that differ from the desired wavelength by
predetermined amounts. In such embodiments, each of the plurality
of detectors is coupled to one of the control waveguides, and
producing channelized RF output signals representative of desired
RF bands includes heterodyning, by each of the plurality of
detectors, the signal from the control waveguide to which it is
coupled with the selected wavelength signal from a respective
output end of one of the ring resonators.
In some embodiments, the desired wavelength must be such that
allows operation at W-band. In such embodiments, the predetermined
amount may be 75 GHz. In other embodiments, at least one of the
ring resonators includes a plurality of rings. In another
embodiment, the ring resonators comprise micro ring resonators. In
yet another embodiment, the method includes creating the signal for
the input waveguide by modulating, by an optical modulator, an
inputted optical carrier signal with a received signal. In a
further embodiment, receiving the signal from the input waveguide,
filtering the signal, receiving the second signal, and producing
channelized RF output signals occur on a single chip.
The above summary is provided merely for purposes of summarizing
some example embodiments to provide a basic understanding of some
aspects of the invention. Accordingly, it will be appreciated that
the above-described embodiments are merely examples and should not
be construed to narrow the scope or spirit of the invention in any
way. It will be appreciated that the scope of the invention
encompasses many potential embodiments in addition to those here
summarized, some of which will be further described below.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus described certain example embodiments of the present
disclosure in general terms, reference will now be made to the
accompanying drawings, which are not necessarily drawn to scale,
and wherein:
FIG. 1 illustrates a schematic diagram of a micro-ring resonator
(MRR), in accordance with some example embodiments;
FIG. 2 illustrates another diagram of a MRR, in accordance with
some example embodiments;
FIG. 3 illustrates a MMR having 3 rings, in accordance with some
example embodiments;
FIG. 4 illustrates a MMR having 6 rings, in accordance with some
example embodiments;
FIG. 5 illustrates a schematic diagram of an integrated optical
channelizer;
FIG. 6 illustrates a schematic diagram of an example optical
channelizer using a separate control waveguide, in accordance with
some example embodiments;
FIG. 7 is a graphical representation of example spectra at several
key junctions of downconversion for two optical channelizer
channels, in accordance with some example embodiments;
FIG. 8 illustrates a schematic diagram of an example optical
channelizer using multiple control waveguides, in accordance with
some example embodiments; and
FIG. 9 illustrates a flowchart describing example operations for
using an integrated optical channelizer for detecting W-band
signals, in accordance with some example embodiments
DETAILED DESCRIPTION
Some embodiments of the present invention will now be described
more fully hereinafter with reference to the accompanying drawings,
in which some, but not all embodiments of the inventions are shown.
Indeed, these inventions may be embodied in many different forms
and should not be construed as limited to the embodiments set forth
herein; rather, these embodiments are provided so that this
disclosure will satisfy applicable legal requirements. Like numbers
refer to like elements throughout.
In conjunction with the attached Figures, a signal channelizer 10
is herein described having an input waveguide 14 configured to
carry an inputted signal having a plurality of wavelengths that
includes at least one desired center optical wavelength. The input
waveguide 14 is connected to an integrated Optical Modulator (TOM)
42 which has an input port 22 for receiving an unmodulated
continuous wave (CW) optical signal 40, an input RF port 60 for
receiving the wideband RF signal 58 to be channelized, and which is
configured to create the inputted signal transmitted using the
input waveguide by modulating the optical signal 40 with the
wideband RF signal 58. After modulation of the CW optical signal,
the wideband RF signal appears as a plurality of optical
wavelengths 20, as shown in FIG. 1.
A plurality of ring resonators 12 for wavelength selection are
arranged in parallel and coupled at spaced apart locations along
the input waveguide 14 for receiving the inputted signal from the
input waveguide 14. In this regard, coupling a ring resonator 12 to
the input waveguide 14 may comprise moving the ring resonator close
enough to the waveguide that, due to the wave property of light,
some fraction of the light from the waveguide will enter the ring
resonator. Each of the plurality of ring resonators 12 is then
configured to pass a selected wavelength signal to its respective
output end 56, which is opposite the end of the ring resonator that
receives the selected wavelength signal. An output or control
waveguide 16 carries the unmodulated CW optical carrier, which has
been stripped from all modulation after passing through a very
narrow optical ring resonator filter 12X. The output waveguide 16
passes or communicates a desired portion of the CW optical signal
to the output end 56 of each ring resonator 12. In some
embodiments, an output waveguide 16 is tapped with couplers 46 for
providing the desired portion of the CW optical carrier to feed the
output end 56 of the ring resonators 12 with the desired CW optical
carrier. An optical detector 32 associated with the output end 56
of each ring resonator 12 produces the desired output RF filtered
(or channelized) signal 34. The result is that the ring resonators
12 provide desired wavelength filtering of the inputted signal and,
after mixing with the optical carrier, the detector or detectors 32
channelize the output signal 34 into desired RF components.
The IOC 10 is based on photonic micro-ring resonators (MRRs) 12,
thus the operation of MRRs may be briefly summarized as follows.
Photonic MRRs 12 are versatile wavelength-selective devices that
can be used to synthesize a wide range of photonic filtering
functions.
As shown in FIG. 1, a MRR 12 consists of two parallel optical
waveguides 14, 16 with a ring waveguide 18 in between them. In a
MRR 12, multiple optical wavelength signals 20 enter at the input
port 22 (Terminal 1) of the "bus" waveguide 14. Of those
wavelengths, one will be coupled into the ring 18 via Coupler 1 24.
Next, the optical signal in the ring 18 will be coupled into the
"control" waveguide 16 via Coupler 2 26.
The degree to which coupling is achieved depends on the resonant
condition: n.sub.effL=m.lamda., where n.sub.eff is the effective
refractive index of the bending waveguide, L is the circumference
of the ring 18, .lamda. is the optical wavelength, and m is an
integer. When optical wavelength .lamda..sub.i satisfies the above
condition, it will be coupled 100% from the bus waveguide 14 to the
control waveguide 16, while all other wavelengths that do not
satisfy the above condition will continue into the bus waveguide 14
with virtually zero attenuation and exit at output Terminal 4
28.
This filtering operation is also explained in FIG. 2 (note the
extremely small dimension of the ring, on the order of 50 microns).
This small size manifests the fact that the size of a filter scales
with the carrier wavelength and optical components are orders of
magnitude smaller than their RF equivalents. The filtration of the
signal occurs due to the size of each resonator 12 (or, in some
embodiments, by manipulation of other physical characteristics that
may be known to alter resonance). In particular, as light passes
through the ring resonator 12, the selected wavelength signal
undergoes constructive interference each time it passes a given
point on the circumference of the ring resonator 12. Other
wavelengths, however, will not be at resonance within the ring
resonator 12, and therefore will not be efficiently coupled to from
the input 14 to the output end 16.
To further increase the "fitness" or coupling selectivity of the
ring, two or more rings 18a-18c can be used, as shown in FIG. 3
(having three rings) and 4 (having six rings).
In some embodiments, MRRs 12 can be made in various substrates
using conventional optoelectronic foundries, e.g., SiO.sub.2
(Silicon Dioxide), InP (Indium Phosphide), and various forms of
glass-like materials. Such devices have been made as small as a few
.mu.m in size and are thus ideal for large scale integration.
The present IOC 10 may combine photonic up-conversion, combined
on-chip photonic MMR filtering, on-chip square law detection, and
downconversion to create a very powerful RF channelizer. Further,
the IOC 10 of an example embodiment of the present invention may
advantageously employ one or more of the following operations: (1)
up-conversion of the RF band of interest by modulating an optical
carrier with the received RF signal; (2) multi-channel filtering in
the optical domain (via multiple MRRs) with GHz-type resolution;
and (3) downconversion of the filtered MRR outputs via mixing with
the optical carrier and subsequent square-law detection.
FIG. 5 shows an example single-chip architecture embodiment in
which the IOC described above is contained on a single chip. With
the aid of FIG. 5, one can understand the present IOC 10 via its
three key operations as follows.
Optical up-conversion: The input RF signal 58 to be channelized
modulates an optical carrier 40 using an external Integrated
Optical Modulator 42 (TOM). As described below, an on-chip
heterogeneously-integrated TOM 42 is also possible.
Photonic filtering: The RF-modulated optical carrier 40 enters the
"bus" waveguide 14 of an integrated optical channelizer structure
10. As it propagates it encounters N different multi-order MRRs
12A-12N that are designed to "sharply" band-pass-filter a narrow
band of light (Mi) over the full RF modulation F.sub.full and are
connected in a parallel arrangement along the bus waveguide 14. The
center frequency (f.sub.c) of these filters increases by .DELTA.f,
such that N.times..DELTA.f=F.sub.full. For example, to cover the
2-18 GHz band with 20 MRR filters each with .DELTA.f=0.8 GHz, the
MRR-to-MRR f.sub.c must increase by 0.8 GHz.
Carrier mixing and detection: In FIG. 5, the last MRR filter 12X
before the terminus (absorber) 54 of the bus or input waveguide 14
deals exclusively with the optical carrier or "bias" wavelength
.lamda..sub.c; specifically, it separates it from any other
unfiltered signals and guides it into the control waveguide 16. The
control waveguide 16 of FIG. 5 acts as a "bias" bus 44 that one
"taps" with couplers 46 in order to feed the output from the output
end 56 of each MRR filter 12A-12N to mix the filtered sideband with
the carrier 40.
This "feeding" is accomplished using on-chip variable ratio optical
couplers 46. The "variable" ratio is needed in order to feed the
output of each MRR 12A-12N with approximately the same amount of
carrier optical power. Thus, as the control waveguide 16 goes from
right to left in FIG. 5, the ratio of each coupler 46 increases
because less and less light is available. In some embodiments, the
same operation could be achieved by "equally" splitting the control
waveguide output into N channels, and then directing each channel
to a different MRR. However, the 1-to-N splitter approach increases
the complexity and size of the IOC. The N-output waveguides which
carry both the N-channels of the filtered modulation and N-equal
power carrier portions end up in an on-chip integrated square law
detector 32A-32N (DET, in FIG. 5). The detectors can be either
heterogeneously integrated onto the chip or they can be
grown/deposited directly onto the chip. In another embodiment, the
detectors can be external to the chip.
As FIG. 5 shows, the dimensions of the IOC 10 are extremely small.
Since typical resonators, made in, for example, silicon or silicon
oxynitride, are separated by about 250 microns and are about 50
microns in diameter, a 20 channel 5th order MRR IOC will occupy
.about.5.5 mm.times.0.5 mm (again, this is due to the fact that the
size of a filter scales with the carrier wavelength). Thus, the IOC
10 of FIG. 5 could accomplish functions that commercial
off-the-shelf (COTS) RF channelizers require more than 10 square
inches to accomplish.
IOC 10, disclosed above, is in essence a high resolution filter
bank and thus can be used as a cueing receiver, a radar warning
receiver, or for any number of additional purposes. The IOC 10
occupies a few square millimeters; it can have 10s of fixed and/or
tunable channels with various bandwidths (0.5-25 GHz). Since any of
its filters can be tuned anywhere in this 4,000 GHz band, it can be
used for threat detection in the millimeter wave (mmW) spectrum,
and specifically in the W-band (75-110 GHz). This is very important
because there is simply no other miniature channelizer technology
with a 100% probability of intercept that can cover the W-band
which is considered the latest "new" threat band.
However, there are two peripheral component issues that prevent the
IOC architecture of FIG. 5 from being truly practical at the
W-band: (1) RF down converters needed for the conversion of the
W-band to, for example, a Ka baseband, and (2) COTS photodiodes
(DET) that can operate efficiently with 75-110 GHz signal input.
The former deficiency relates to the fact that the DET outputs of
the IOC in FIG. 5 are physically W-band signals. Therefore, in
order to be digitized and processed with existing digital signal
processor (DSP) technology, the W-band outputs need to be converted
first to a lower RF band and subsequently to a baseband. However,
parallel, multi-channel downconversion from the W-band to, for
example, the Ka band (40 GHz) is historically a very difficult task
requiring mmW mixers, filters, bulk waveguides, mmW local
oscillator (LO) generators, and low noise amplifiers (LNAs), among
other components. The second problem is that there currently exists
a lack of COTS efficient, low cost, mmW photodiodes. In addition,
the small area associated with mmW photodiodes restricts the
maximum incident optical power which limits the gain and thus the
signal-to-noise ratio (SNR) of the IOC.
Accordingly, a new optical downconverting IOC architecture is
needed to solve both of these problems. The
optically-downconverting optical channelizer described below
provides a global solution in which a band within the 4,000 GHz IOC
BW can be downconverted and detected using truly COTS-based optical
components.
FIG. 6 illustrates a schematic diagram of an example optical
channelizer that addresses these issues and accordingly is
configured for detection of a W-band input signal 62. The example
IOC shown in FIG. 6 is similar in certain respects to that
described in FIG. 5 above. For instance, the IOC described in FIG.
6 also has an input waveguide 14 and a plurality of ring resonators
12A to 12N for wavelength selection. In this regard, the ring
resonators are arranged in parallel and coupled at spaced apart
locations along the input waveguide 14 for receiving the inputted
signal 20 from the IOM 42 via the input waveguide 14. Each of the
plurality of ring resonators 12 is configured to pass a selected
wavelength signal to its respective output end 56. Similarly, a
control waveguide 16 is tapped with couplers 46 to feed the output
ends 56 of the ring resonators 12 with the signal carried by the
control waveguide 16. Finally, optical detectors 32A to 32N,
associated with the output ends 56 of each ring resonator 12,
produce the desired output RF filtered (or channelized) signal 34.
The result is that the ring resonators 12 provide desired
wavelength filtering of the inputted signal 20 and, after mixing
with the optical carrier, the detector or detectors 32 channelize
the output signal into desired RF components.
However, the IOC shown in FIG. 6 has several major differences from
the architecture shown in FIG. 5 including, but not limited to: (1)
the control waveguide 16 is separated from the bus waveguide; (2)
the control waveguide 16 is injected with continuous wave (CW)
laser light 64 at wavelength .lamda..sub.B, which may differ from
the wavelength (.lamda..sub.A) used for the signal detection and
the bus waveguide by a predetermined amount (which may be based on
the number of filters included in the IOC and the RF bandwidth for
which detection is required); and (3) the photodiodes used at the
IOC output channels need not operate at the 110 GHz that the
original IOC would require.
With respect to differences (1) and (2), the control waveguide 16
is configured to carry a second signal having a wavelength that
differs from the desired wavelength by the predetermined amount. By
using a different wavelength of light in the control waveguide,
each square law detector DET 32, upon detection of the two
different wavelength light beams, will heterodyne the signals to
effectively generate their RF difference frequency at its output
34, which, as described in greater detail below, will comprise RF
output signals representative of desired RF bands. With respect to
difference (3), the photodiodes need not operate as high as the 110
GHz upper threshold of the W-band, because the heterodyning
operation downconverts the RF output by the difference between
wavelengths .lamda..sub.A and .lamda..sub.B, which may be freely
chosen.
FIG. 7 shows a graphical illustration including example spectra at
several key junctions of the downconverting IOC architecture for
the first (75 GHz) and last (110 GHz) IOC channels. The CW laser
light 702 at wavelength .lamda..sub.A is double-sideband (DSB)
modulated by the input W-band (75-110 GHz) signal 704 via the
integrated optical modulator (IOM). The spectrum 706 at the IOM's
output therefore includes some DC light at .lamda..sub.A as well as
2 sidebands which cover the f.sub..lamda.A-75 GHz to
f.sub..lamda.A-110 GHz (lower sideband) and f.sub..lamda.A+75 GHz
to f.sub..lamda.A+110 GHz (upper sideband). The MRR filters of the
IOC are single sideband (SSB) and, in this example, have a 1 GHz RF
BW each (e.g., 35 such filters are needed to cover the 75-110 GHz
band with 1 GHz resolution).
For ease of explanation, FIG. 7 only shows example spectra of the
1st and last (35th) IOC channels. The 1st IOC channel covers the
75-76 GHz band (shown as .lamda..sub.A+75 GHz in FIGS. 6 and 7),
whereas the 35th channel covers the 109-110 GHz band (shown as
.lamda..sub.A+110 GHz in FIGS. 6 and 7). The MRR filters block the
lower sideband as well as the DC light and pass only a portion of
the upper sideband to an output end of the MRR. Thus, as shown in
spectrum 708, at the bottom of the 1st MRR filter light exists only
in the .lamda..sub.A+75 GHz to .lamda..sub.A+76 GHz band (denoted
as .lamda..sub.A+75 GHz in FIG. 7) whereas at the bottom of the
35th filter, shown by spectrum 710, light exists only in the
.lamda..sub.A+109 GHz to .lamda..sub.A+110 GHz band (denoted as
.lamda..sub.A+110 GHz in FIG. 7).
Next the filtered light is mixed with the CW laser light 712 at
wavelength .lamda..sub.B and is detected by each DET to produce
channelized RF output signals representative of desired RF bands.
In this regard, the square law detection process heterodynes the
second signal from CW laser light 712 with the filtered light (the
wavelength signal from the output end of the ring resonator), which
results in the generation of both the sum and the difference of the
filtered light and the CW light at .lamda..sub.B. However, the sum
at (f.sub..lamda.B+.sub..lamda.A+k GHz) is outside the DET BW and
thus it produces no output. Given the fact that
f.sub..lamda.B-f.sub..lamda.A=75 GHz, the difference term
(-f.sub..lamda.B+f.sub..lamda.A+k GHz) becomes
(-f.sub..lamda.B+f.sub..lamda.A+k GHz)=(-f.sub..lamda.A-75
GHz+f.sub..lamda.A+k GHz)=k-75 GHz, which is the desired
downconverted RF output. For example, for the first channel with
k=75 to 76 GHz the resulting RF output is 0-1 GHz (spectrum 714),
whereas for the 35th channel with k=109-110 GHz the resulting RF
output is 34-35 GHz (spectrum 716). Accordingly, by downconverting
W-band signals into the Ka band, example embodiments of the present
invention can avoid the use of tremendous amounts of expensive and
bulky W-band mmW hardware, while at the same time producing
accurate results using COTS, low cost 35 GHz frequency photodiodes
(in contrast to 110 GHz DETs, which are not currently commercially
available).
The concept described in FIGS. 6 and 7 can additionally be modified
to introduce additional control waveguides, in situations where it
is desirable to downconvert the W-band to lower-than-Ka RF bands.
Turning now to FIG. 8, a schematic diagram of an example optical
channelizer is illustrated that uses multiple control waveguides.
In the example shown in FIG. 8, two control waveguides 16 and 68
are used, such that the W-band is downconverted into 2 sets of Ku
band (18 GHz) outputs. In this example, the laser light 64 at
wavelength .lamda..sub.B satisfies f.sub..lamda.B-f.sub..lamda.A=75
GHz, whereas a second laser light 66 at new wavelength
.lamda..sub.C satisfies f.sub..lamda.C-f.sub..lamda.A=94 GHz. As
FIG. 8 shows, wavelength .lamda..sub.B is transmitted along a first
control waveguide 16 and is used by the first 18 channels to
downconvert the 75-93 GHz part of the W-band to the 0-18 GHz Ku
band. Note that the control waveguide 16 with wavelength
.lamda..sub.B terminates at channel #18. Wavelength .lamda..sub.C
on the other hand, enters a separate control waveguide 68, mixes
with channel #19 (94 GHz) as well as with the remaining channels
beyond #19, and terminates at channel #35 (110 GHz). Because its
relationship with wavelength .lamda..sub.A is
f.sub..lamda.C-f.sub..lamda.A=94 GHz, it downconverts channel #19
into the 0-1 GHz part of the Ku band, channel #20 into the 1-2 GHz
band, and so forth, with the last channel (#35) being converted to
the 15-16 GHz band. In this fashion, the example shown in FIG. 8
illustrates the use of two sets of 18 GHz photodiodes to cover the
full W-band. Accordingly, downconverting W-band signals into the Ku
band can expand upon the benefit of using low cost COTS
photodiodes, by enabling the use of photodiodes having lower
frequencies than 35 GHz. Although two control waveguides are used
in the example shown in FIG. 8 in conjunction with 18 GHz
photodiodes, in other embodiments additional waveguides may be used
to downconvert the W-band signals further, which may enable the use
of photodiodes having yet lower frequencies.
Turning now to FIG. 9, operations performed by the above-described
IOC will be described in connection with the illustrated flowchart
of operations for detecting W-band signals.
In operation 902, the IOC includes means, such as, input waveguide
14 of FIG. 5, 6, or 8, for receiving an inputted signal having a
plurality of wavelengths including a desired wavelength. As
described above, this inputted signal may be received via IOM 42 of
FIG. 5, 6, or 8, which is configured to modulate CW light 40 of
FIG. 5, 6, or 8, and an input RF signal 58 of FIG. 5, which may
further comprise a W-band RF signal 62, shown in FIGS. 6 and 8.
In operation 904, the IOC includes means, such as the plurality of
ring resonators 12 of FIG. 5, 6, or 8, for filtering the inputted
signal to pass selected wavelength signals to an output end. In
this regard, as described previously, each ring resonator blocks
the lower sideband as well as the unmodulated optical carrier (or
DC light), and accordingly passes only a portion of the upper
sideband to an output end 56 of the ring resonator 12 shown in
FIGS. 5, 6, and 8. In one such embodiment, the plurality of ring
resonators 12 comprise MRRs. In another embodiment, each of the
parallel ring resonators includes a plurality of rings, to further
increase the filter selectivity of the ring resonator.
In operation 906, the IOC includes means, such as a control
waveguide 16 of FIG. 6 or 8, for receiving a second signal having a
wavelength that differs from the desired wavelength by a
predetermined amount. In this regard, the predetermined amount may
be 75 GHz, but may be determined based on the downconversion
desired and the number of detectors included in the IOC. Moreover,
in embodiments of the IOC including a plurality of control
waveguides, this operation may include receiving, by one or more
additional control waveguides (e.g., 16 and 68 of FIG. 8), one or
more signals having wavelengths that differ from the desired
wavelength by predetermined amounts,
Finally, in operation 908, the IOC includes means, such as the
plurality of detectors 32, shown in FIGS. 5, 6, and 8, for
producing channelized RF output signals representative of desired
RF bands. In this regard, each of the plurality of detectors is
coupled to the control waveguide 16 and produces channelized RF
output signals representative of desired RF bands by heterodyning
the second signal with a wavelength signal from a respective output
end 56 of one of the ring resonators, as shown in FIGS. 5, 6, and
8. In embodiments of the IOC including a plurality of waveguides,
each of the plurality of detectors is coupled to one of the control
waveguides, and produces channelized RF output signals by
heterodyning the signal from the control waveguide to which it is
coupled with the wavelength signal from a respective output end 56
of one of the ring resonators.
The above description illustrates the use of multiple optical
wavelengths in conjunction with a modified IOC architecture in
order to detect and down convert W-band into Ka, Ku, or even lower
bands. As a result, embodiments of the present invention avoid the
need to use tremendous amounts of expensive and bulky W-band mmW
hardware while at the same time using COTS, low cost 35 GHz, 18 GHz
or lower frequency photodiodes (in contrast to 110 GHz DETs, which
are not currently commercially available).
As described above, FIG. 9 illustrates a flowchart of the operation
of the above-described IOC according to example embodiments of the
invention. It will be understood that in some embodiments, certain
ones of the operations above may be modified or further amplified.
Furthermore, in some embodiments, additional optional operations
may be included. Modifications, amplifications, or additions to the
operations above may be performed in any order and in any
combination.
In this respect, many modifications and other embodiments of the
inventions set forth herein will come to mind to one skilled in the
art to which these inventions pertain having the benefit of the
teachings presented in the foregoing descriptions and the
associated drawings. Therefore, it is to be understood that the
inventions are not to be limited to the specific embodiments
disclosed and that modifications and other embodiments are intended
to be included within the scope of the appended claims. Moreover,
although the foregoing descriptions and the associated drawings
describe example embodiments in the context of certain example
combinations of elements and/or functions, it should be appreciated
that different combinations of elements and/or functions may be
provided by alternative embodiments without departing from the
scope of the appended claims. In this regard, for example,
different combinations of elements and/or functions than those
explicitly described above are also contemplated as may be set
forth in some of the appended claims. Although specific terms are
employed herein, they are used in a generic and descriptive sense
only and not for purposes of limitation.
* * * * *